Setting aside a magnetic memory, a semiconductor device such as an integrated circuit is fabricated such that it is generally formed on a wafer, separated from the wafer, and then, is assembled as an electronic part, followed by packaging. In an inspection process, a probe test is carried out to confirm the operation of each of the devices formed on the wafer before the devices are cut out.
In the probe test, a prober is used. The prober has a prober chuck for retaining a wafer therein and a stage for relatively moving the chuck with respect to a needle in contact with the wafer. First of all, the wafer is placed and retained on the chuck, an electrode of a semiconductor device and a needle are brought into contact with each other by the operation of the stage, an electric signal is supplied from a tester to the device via the needle, and then, a signal output from the device is detected by the tester, thus inspecting whether or not the device is normally operated.
In order to achieve low leakage evaluation, Patent Document 1, for example, discloses, as a low leakage chuck capable of measuring a fine current with high accuracy, a chuck for a prober including a conductive chuck top having a wafer placed thereon, an insulating member for retaining the bottom surface of the conductive chuck top, and a guard layer made of a conductive material such as nickel plating formed on the lower surface of the insulating member. Here, the same potential is applied to both of the conductive chuck top serving as a signal layer in contact with the back surface of the wafer and the guard layer, thus suppressing a leakage current flowing from the signal layer to a ground layer (i.e., an earth), not shown.